Electrical contact materials dispersed with metal oxides, particularly cadmium oxides or tin oxides in silver matrices are widely employed in the electrical industry today.
Such silver-metal oxides electrical contact materials are generally produced either by a powder metallurgical method or internal oxidation method. In the powder metallurgical method, silver powders which constitute matrices of a contact material and powders of metal oxides are mixed at a desired ratio, and are sintered at a temperature below the melting points of constituent metals after having been molded into a green compact, while in the internal oxidation method, after a molten alloy of silver and solute metal(s) of a specific amount has been cast and pressed into a desired shape of a certain thickness, the alloy is subjected to internal oxidation so that the solute metal(s) is selectively oxidized.
Such silver base electrical contact materials prepared either by the powder metallurgical method or internal oxidation method are certainly improved of their refractoriness on account of the dispersion of metal oxides in silver matrices. However, they are not free from certain drawbacks. To wit, those prepared by the powder metallurgical method are brittle and hence lack in elongation. Their lives are inferior to those prepared by the internal oxidation method. On the other hand, those prepared by the internal oxidation method are good in elongation and have a high conductivity, while their solute metals are limited for amount and kind. In addition, the dispersion and size of metal oxides precipitated in or about silver matrices are not so even as those prepared by the powder metallurgical method.
Hence, it is an object of this invention to provide an electrical contact material having a good elongation and high conductivity, silver base of which has been melted and solidified presenting a continuous matrix, and fine particles of metal oxides, particularly tin oxides and/or tin alloy oxides of 4-25 weight % being dispersed uniformly throughout said silver matrix.
It is another object of this invention to provide a method or preparing the aforementioned kind of electrical contact materials.